...except that almost every table in existence has something that messes up the system. Usually it's an upper limit on the amount you can bet (called a "table limit"), which puts an upper bound on the number of successive losses you can win back.
The wikipedia article[1] covers this relatively well under "An alternative mathematical analysis."
The short of it, though, is that everything at a casino is there to put the odds in the house's favor. They spend enormous amounts of time and money on researching this very problem, and their entire business depends on carefully walking the space between their patrons having a good time and winning a mint.
[1] http://en.wikipedia.org/wiki/Martingale_(betting_system)